Hundreds of American women are being ensnared by Internet scammers based in Malaysia, with some losing over a quarter of a million dollars, as the country becomes an epicenter for online crime perpetrated by Africans, U.S. officials say.

The mostly Nigerian conmen, who enter Malaysia on student visas, take advantage of the country's good Internet infrastructure to prey on lonely, middle-aged women, wooing them on dating websites before swindling their savings, they said.

The scams are more sophisticated than most Nigeria-based operations - which most Internet users have experienced at some time either via email or advertising - helped by Malaysia's advanced banking system, which allows perpetrators to quickly set up accounts and receive international transfers.

U.S. officials say Malaysian police lack the resources and expertise to tackle the problem and have yet to launch a single prosecution of a case involving a U.S. victim.

Malaysian police were reported by local media last December as saying that the number of Internet scam cases more than doubled in 2013 with total losses of more than $11 million. A total of 476 Africans had been apprehended for suspected involvement, the report said.

The Malaysian police and the Nigerian embassy in Kuala Lumpur did not respond to Reuters' request for comment. A spokesman for Nigeria's Economic and Financial Crimes Commission said he was not aware of scammers operating in Malaysia, but added they were known to have international networks.

Tim Scherer, consul general at the U.S. embassy in Kuala Lumpur, told Reuters that complaints about such scams now made up more than 80 percent of inquiries to duty officers at the mission, with a dozen new cases reported every week.

Citizens of Australia, Canada and Europe had also been targeted, he said.

"These are not rich widows who are being preyed on, these are middle-class Americans who don't have this kind of money to spare," he said. "It can really transform their lives in a very terrible way."

The U.S. embassy estimates that U.S. victims are losing several million dollars a year, with two women in the past 12 months losing more than $250,000 each. There are more than 600 cases a year, and the amount lost by each victim averages in the tens of thousands of dollars, it said.

The actual figure of total losses is probably far higher, Scherer said, because many victims are too embarrassed to come forward or do not know who to contact. He said the scammers were highly sophisticated, often grooming victims for months and using convincing techniques such as forging letters purportedly from the U.S. ambassador in Malaysia.

Fake romance

Large teams of scammers typically trawl dating or Christian websites and contact middle-aged women, the U.S. officials said. They pretend to be a Western man who then gets into legal or business difficulties in Muslim-majority Malaysia.

One U.S. victim told Reuters she transferred a total of$260,000 to Malaysia, where the man who claimed to love her said he was being prevented from returning to the United States by Malaysian bureaucracy - which required hefty payments to negotiate.

The 59-year-old widow from Phoenix, Arizona, who declined to be identified, said she had gone heavily into debt to make the payments to "Charles", and even flew to Malaysia in March to meet him. He never showed up, but a European woman claiming to be his lawyer managed to bilk another $25,000 out of the woman before she returned to Arizona.

Another victim, a women in her late 50s in the eastern United States, said she sent her life savings of $300,000 over two months to a Malaysia-based "American" man she met on dating site Match.com, three years after her husband died.

"I felt like I was in love with this man and we'd be moving forward with a life together real soon," she told Reuters.

Match.com did not respond to a Reuters request for comment. Along with other major U.S.-based dating sites, it features prominent warnings about scammers, specifically telling users to be wary of people who say they are Americans based abroad.

Student scam

The conmen have exploited Malaysia's drive to become a global education hub, securing student visas to attend college, the U.S. officials said.

Malaysia has pursued a policy of attracting international students for more than a decade, allowing dozens of foreign colleges to set up Malaysian campuses.

Scherer said it was likely that many of the Nigerians in Malaysia were not genuine students. As of March, there were 9,146 Nigerians on student visas in Malaysia, the education ministry said, out of 123,000 overseas students in total.

"Once in the country as students, there's very little effort to verify their studies," Scherer said.

An official with Malaysia's education ministry said that last year it tightened its vetting and tracking of overseas students.

"We are aware of problems with some international students, especially Nigerians," the official said.